P229F: NOx Sensor Circuit Range/Performance (Bank 1 Sensor 2)

P229F says the rear NOx sensor on bank 1 is electrically sound but its reading fails a plausibility test. Methods vary. GM's 6.6L LML waits for a burst of engine-out NOx and faults the sensor if its own value moves by less than 3 ppm (Type B); the 3.0L LZ0 watches the stability of the internal pump currents, failing above 0.5 percent unstable time. Ford checks offsets of roughly 30 ppm low or 50 ppm high and a missing rise on tip-in; VW's 2014 Touareg TDI checks offset, self-diagnosis results and oxygen plausibility. Volvo and Mack explain that P229F-64 can set when a fresh SCR leaves almost no NOx, so a single event is no proof of a bad sensor. Hino wants DEF quality and dosing checked first, and Ford warns that EGR cleaning fluids poison NOx sensors.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

• Malfunction indicator lamp on
• Often stored together with SCR efficiency code P20EE
• Downstream NOx value implausible compared with the upstream sensor

Most likely causes

• Outlet NOx element drifted, slow or poisoned (e.g. sodium from cleaning fluids)
• Poor DEF quality or faulty dosing that distorts downstream NOx
• Harness or connector fault at the outlet sensor (Volvo/Mack P229F-64)
• Engine or dosing software needing an update (several FCA, Hino, Mazda notices)

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes and the NOx data before and after the SCR catalyst
2. Compare the reading with other engine data while varying the engine speed.
3. Check the sensor's connector and wiring
4. Look for exhaust leaks ahead of the sensor
5. Confirm that the AdBlue/DEF is of good quality
6. Replace the sensor only after ruling out power, ground, and leaks

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P229F means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 2: Fuel injection
• 9F: Specific fault in that system

Frequently asked questions

Can I keep driving with code P229F?

You can keep driving in moderation because the engine does not usually notice it. Get it checked before long, since some cars start a countdown that ends up preventing starting.

What causes code P229F?

The most common causes are: outlet NOx element drifted, slow or poisoned (e.g. sodium from cleaning fluids); poor DEF quality or faulty dosing that distorts downstream NOx; harness or connector fault at the outlet sensor (Volvo/Mack P229F-64).

Related codes

• P229ENOx Sensor Circuit (Bank 1 Sensor 2)
• P22A0NOx Sensor Circuit Low (Bank 1 Sensor 2)
• P22A1NOx Sensor Circuit High (Bank 1 Sensor 2)
• P2201NOx Sensor Circuit Range/Performance (Bank 1 Sensor 1)
• P221ANOx Sensor 1/2 Correlation (Bank 1)
• P225ENOx Sensor Performance - Signal Biased/Stuck High (Bank 1 Sensor 2)
• P225FNOx Sensor Performance - Signal Biased/Stuck Low (Bank 1 Sensor 2)
• P22FENOx Sensor Performance - Sensing Element (Bank 1 Sensor 2)

Sources

• gsi.ext.gm.com: 14OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 25OBDG04A
• fordservicecontent.com: obd summary diesel 2023
• static.nhtsa.gov: MC 10074008 2280

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.